Dispersion is an optical phenomenon in which the phase velocity of a wave depends on its frequency. The most commonly understood example of dispersion is a rainbow, in which dispersion causes spatial separation of a generally white light into a plurality of different colors that are defined by the varying wavelengths present in white light. In optical systems, dispersion may cause pulses to generally spread within communication media through which the pulse is transmitted, e.g., optical fibers. Dispersion may thereby generally degrade signals, especially those transmitted over long distances. Accordingly, dispersion in optical communications systems should generally be corrected or compensated.
Known dispersion compensation systems employ a three dimensional mirror that defines a curved surface opposite the mirror. The mirror reflects an incoming optical signal through the curved surface to generally correct for any dispersion in the signal. The curved surface defines a concave portion and a convex portion separated by a transitional portion therebetween. The curvature of the three portions changes gradually across the curved surface, thereby allowing for different curvatures to be applied to the signal to provide varying amounts of positive or negative dispersion compensation.
Three-dimensional mirrors are limited by their curvature, however, in the amount of dispersion compensation they can apply to an incoming optical signal. Three-dimensional mirrors are also difficult to manufacture without imperfections that may cause undesirable signal degradation. Three-dimensional mirrors also necessarily apply compensation in a symmetrical manner, and therefore may overcorrect or undercorrect dispersion where dispersion is not symmetrical in a signal, e.g., where dispersion is concentrated at certain wavelengths. Further, no adjustment of the dispersion compensation is possible beyond the range of two-dimensional curves provided by the curved surface of a three-dimensional mirror.
Accordingly, there is a need for an improved system for compensating signal dispersion that allows for more accurate compensation and simplified manufacturing.